In recent years, the viewpoint of friendliness to the environment raises concerns on noise problems higher and increases needs to solving the noise problem even for OA machines in offices. Accordingly, sound reduction of OA machines has been intended and actually such the sound reduction has been advanced more than before.
There are several technologies disclosed to solve such the noise problems. For example, JP 9-193506A publication discloses a technology using a noise-masking device which reduces discomfort of noises from a laser beam printer or a copier. The noise-masking device comprises a sound generator which generates a masking sound to mask noises from a drive mechanism that serves on operation as a noise source. The device also comprises a masking sound controller unit which controls and allows the sound generator to generate the masking sound having frequencies within a range that contains major component frequencies of the noises.
However, the technology disclosed in the JP 9-193506A publication has a disadvantage because it adds the masking sound to noisy sounds caused functionally from the body without reducing the noisy sounds, resulting in an elevated noise level. Therefore, some persons may feel rather noisy and more uncomfortable. In addition, the technology requires the use of the sound generator which generates the masking sound and the controller which controls the masking sound to be generated for a limited time period, during which the sounds to be masked are caused. Therefore, the technology also has a disadvantage because it requires, on layout of the machine, an extra space and greatly elevated cost.
Technologies relating to apparatus and methods of evaluating sound quality are also disclosed as described below. For example, JP 10-232163A publication discloses a technology for facilitating of determination on a relation between a noise and the corresponding psychological noisiness. This technology is employed, in an apparatus and method of evaluating sound quality, for evaluating only a “roaring sound” among noises consisting of sounds with many tones from image forming apparatus. The roaring sound is a heavy noise with low-frequency random noises caused from an air flow system, such as an exhausting sound.
JP 10-253440A publication discloses a technology, in an apparatus and method of evaluating sound quality, for evaluating only a “screeching sound” extracted from noises consisting of sounds with many tones from image forming apparatus. The screeching sound is a continuous pure sound caused from a scanner motor or a charger and is recognized noisy.
JP 10-253442A publication discloses a technology, in an apparatus and method of evaluating sound quality, for evaluating only a “friction sound” extracted from noises consisting of sounds with many tones from image forming apparatus. The friction sound is composed of high-frequency random noises caused from slipping of a recording paper.
JP 10-267742A publication discloses a technology, in an apparatus and method of evaluating sound quality, for evaluating only a “whir” extracted from noises consisting of sounds with many tones from image forming apparatus. The whir is composed of pure sounds that have peaks at a plurality of frequencies proximate to a humming from a drive system.
JP 10-267743A publication discloses a technology, in an apparatus and method of evaluating sound quality, for evaluating “smoothness” of a sound extracted from noises consisting of sounds of many tones from image forming apparatus. When there is no pure sound and humming, that is, no projected component is present in a frequency waveform, a person can feel such the sound as a smooth sound. Therefore, it is possible to totally call noisiness felt by a person as “smoothness”.
The above conventional technologies in terms of the apparatus and method of evaluating sound quality, however, failed to propose any apparatus and method of improving sound quality on actual products though they propose the methods of evaluating sound quality.
Currently, an acoustic power level (ISO 7779) is generally employed in OA machines as an approach which evaluates a noise. The acoustic power level is a value of acoustic energy produced from an office machine such as a copier and a printer. Accordingly, there may be often no well correlation between the acoustic power level and a human subjective discomfort against the noise. For example, when sounds with the same acoustic power level are heard and compared with each other, a difference in discomfort between them may be found. In addition, even if a sound has a low acoustic power level, a person may feel the sound extremely uncomfortable.
Accordingly, a further improvement on the office environment requires reduction of the acoustic power level of an OA machine as well as progression in improvement on its sound quality. The improvement on the sound quality requires a quantitative measurement of the sound quality to grasp the current situation and a measurement of an improved degree after the improvement. However, the sound quality is not a physical quantity and accordingly can not be measured quantitatively. Namely, when sounds are listened to through ears to compare their qualities with each other, a difference may occur in evaluations according to persons. In addition, an expression can be performed only qualitatively such that “the sound quality was improved a little” or “considerably improved”. Unless a quality of a sound can be expressed quantitatively with a physical quantity, even if measures are implemented for improvement on the sound quality, it is impossible to evaluate the effect objectively.
Psychoacoustic parameters are physical quantities employed for evaluating sound quality. Typically, the psychoacoustic parameters include the following (see, for example, The Japan Society of Mechanical Engineering, The 7th Design and Systems Conference, “Direct to innovative leaps in design and systems towards the 21st century!”, Nov. 10 to 11, 1997, “Sounds/vibrations and design, colors and design (1)” division, 089B. Characters in brackets denote a unit).                Loudness (sone), Magnitude of audibility        Sharpness (acum), Relatively distributed quantity of high-frequency components        Tonality (tu), Contents of pure components        Roughness (asper), Roughness of sound        Fluctuation strength (vacil), Humming        
In addition to the above, such machines are launched that can measure the following psychoacoustic parameters.                Impulsiveness (iu), Impulsive property        Relative approach, Fluctuation feeling        
The above psychoacoustic parameters have a trend to indicate an increase in discomfort as either of them increases a quality. Among those, only the loudness is standardized in ISO 532B. As for other psychoacoustic parameters, the same fundamental concept can be applied, however, programs and computations are different from one another due to a unique research according to each measurement instrument maker. Therefore, measured values are slightly different from one another according to maker sin common. It is possible to improve the sound quality through an effort for reducing all of these psychoacoustic parameters.
However, it requires a great effort to prepare measures for all psychoacoustic parameters. Noises caused from OA machines such as copiers and printers are composed of many toned noises due to complexity of their mechanisms. For example, low-frequency heavy sounds, high-frequency screeching sounds and impulsive sounds are caused variably with time from a plurality of sound sources such as motors, recording papers and solenoids.
A person judges these sounds totally and decides whether he/she feels uncomfortable or not. In this case, the person can be considered to weight on a particular part that relates to the discomfort before the decision. In a word, there are psychoacoustic parameters that are greatly effect on the discomfort and psychoacoustic parameters that are less effect on the discomfort, which differ due to tones from machines. For example, in a printer that causes impulsive sounds many times at a high speed, the impulsive sounds are felt the most uncomfortable. On the contrary, in a desktop printer that causes relatively silent sounds at a low speed, as impulsive sounds are caused less, a charging sound caused on AC-charging is felt the most uncomfortable. Thus, uncomfortable parts differ case by case. Accordingly, the low-speed machine and the high-speed machine may have different parts that require improvements on the sound quality. From such the ground, by searching psychoacoustic parameters that have great improvement effects on discomfort and improving the psychoacoustic parameters to improve sound quality efficiently, the above effort can be reduced.
Accordingly, by combining psychoacoustic parameters that have great improvement effects on discomfort, then weighting the psychoacoustic parameters to derive a sound quality evaluative equation, and computing a subjective evaluation value against the discomfort using the sound quality evaluative equation, it is possible to evaluate the sound quality objectively and improve the sound quality. Further, by deciding, for a subjective evaluation value against discomfort, a degree that can eliminate the discomfort, and providing an image forming apparatus that has sound quality improved below the degree, it is possible to solve the noise-related problems in offices.